Skew helical crown gearing



July 10, 1923. 1,461,230

E. sTUBBs ET AL SKEW HELICAL CROWN GEARING Filed July l 1922 PatentedJuly 10, 1923.

UNITED STATES PATENT p OFFICE I EVERARD STUBBS AND EDWIN R. FELLOWS, OFSPRINGFIELD, VERMONT, ASSIGNOBS T0 THE FELLOWS'GEAB SHAPED, COMPANY, OFSPRINGFIELD, VERMONT, A OOR- POBATION OF VERMONT.

Sm HELICAL CROWN GEABING.

Application led 'July 1,

To all whom it may concern.'

United States, residing at Springfield, in the county lof Windsor .andState of Vermont, have invented new and useful Improvements in SkewHelical Crown Gea-rings, of which the following is a specifica,-v

tion.

The present invention relates to gearing; and its general object,broadly and comprehensively stated, is to furnish toothed gearing, theprinciples of which, in various embodiments, ma be applied to urposesand uses for which hitherto posltive gearing has been practicallyunsuitable.

There are many situations in which driving by gears would be highldesirable, but has not been practicall easible because the gear formshereto ore known either. have not permitted of the driven parts beingheld steadily enough when rotated. at the required speeds, or have notpermitted the required speed rati'os in the availablel space, or havebeen excessively noisy or too expensive in cost of production forcommercial use. For illustration of one such situation, we may mentionspinning machines of the ring Spinnin type for producing finished yarn,in whic a large number of duplicate spindles have to be rotated atexcessively high speed from a. common power shaft. The manner in whichsuch spindles must be mounted to prevent objectionable vibrationprecludes arranging the power shaft in the same plane with the spindleswhich it drives, while no gear forms have been known which would permitof a positive gear drive from the shaft to v the spindles in thedirection and at the speed required in the necessary limitations of sace without intolerable noise and vibration. Hence the spindles of suchmachines have always been driven in commercial practice by bands ortapes. In numerous other situations, more or less analogous to theparticular illustration given, parts rotating on non-intersecting andnon-parallel axes could with advantage have been positively gearedtogether if it had been possible to provide suitable gearing, but other1922. serial no...s72,soo.

driving means have had tobe used on account of the lack hitherto ofsuitable gears.

Such gear elements and couples as have been heretofore designed fortransmitting power between non-intersecting shafts have either been socrude and inaccuratezas to create intolerable vibration and noisewhendriven at high speeds, or have beenI of a type excessively expensive tomake, and impossible to produce in the lower ratios of larger to smallerear, or have compelled the shafts to be aced too far apart and have beenunusab e in situations wherethe shafts are reluired to be near together.

In v lew o the foregoing explanation, our object may now be morespecifically sta-ted as being to furnish a gear couple adapted to bemade lin various speed ratios, the members of which may be mounted torotate about non-intersecting axes transverse to one another, but at thesametime relatively near together at any ratio, and the teeth of whichmay be shaped by generating methods so as to mesh together with correctrolling action and proper bearing throughout a substantial len h, andthe commercial production of w ich may be carried out at minimum cost.

The invention consists, then, in a gear couple comprising a helical spurpinion and a crown gear conjugate to such pinion; and it consistsfurther in the crown gear element of the couple as a new article ofmanufacture; such couple and crown gear .having characteristics adaptingthem to accomplish the above stated objects, as will now be explained indetai-lwith reference to the ac companying drawings.

In the pdrawings Y Figure 1 is a face view showing the spu pinionelement, and a part of the crown gear element in mesh therewith, of agear couple embodyingthe invention.

Figure 2 is a perspective view of a fragment of the' crown gear, andFigure 3 is a L -Qg co illustratively in Figure 1, where a represents acrown gear having teeth a', and b represents a spur pinion havinghelical teeth b. The location of the gear axis is indicated at a2 andthe pinion axis by the line b2-b2- These axes, as is clearly shown bythe drawing, are both nonparallel and nonintersecting, but each isperpendicular to a line parallel to the other. At the same time the axisof the pinion is relatively near the axis of the gear, being lessdistant from the latter axis than the circumference of the gear, thatis, the tooth-bearing zone of the gear.

For convenience of descriptive definition we have called this gear askew helical crown gear. It is novel in the form and contours of itsteeth, but its novel characteristics can best be defined with referenceto the pinion and to the method of generation by which its tooth curvesare formed. The pinion, also, although in principle of known character,is specially formed with reference to the relation which it holds to thegear, in that the helix angle of its teeth is established at such valuethat the acting face of each tooth, when in the middle of its arc ofaction, is approximately radial to the gear, within limits of variationpresently set forth. This condition may be otherwise more exactlydefined as follows. Assume that the line c-d is radial to the gea-r andalso perpendicular to the axle of the gear, and that it passes throughthe point indicated at f where the linear speeds of the pinion and ofthe gear are equal and where their momentary directions of travel aremost nearly the same; that is, where the divergence of their directionsof travel is only that due to the skew arrangement of the pinion. Thispoint may be called the common pitch point of the pinion and the gear.Now, with reference to the point and line thus dened, the helix angle ofthe pinion may be considered as such that the active faces of the pinionteeth when at the middle of their arc of action become app roximatelytangent, within limits, at the common p-itch point f, to the radius c-dof the ear which passes through this point. Obviously the absolute valueof this angle,

with respect to the axis of the pinion, de?

pends on the distance that the pinion axis is o'set from the axis of thegear.

The limits of possible variation of the pinion teeth, from theapproximately radial relation to the gear, heretofore defined, aredetermined by the occurrence of interference between the pinion and theinner ends of the gear teeth, or rather by occurrence of need forundercutting the faces of the gear teethy at these ends in order toavoid interference. That is, the teeth of the gear must have correctface curves, conjugate to the teeth of the pinion at the dista-nce ofthe common pitch point f from the center of the gear. Assuming that thecurved line g re resents a cylindrical surface coaxial with tiie gearaxis a2 and passing through the common pitch point f, then the pinionteeth must not be inclined either way from the radius c-d so far aswould require cuttin away of the face curves of the gear teet betweenthe line g and the center of the gear, to avoid interference. Widerlimits of possible variation are found in the case of the la'rger ratiosof gear to pinion than with the smaller ratios. Without intending tostate any exact limits, but rather by way of illustration, we may saythat when the ratio of the gear to the pinion is as large as four orfive to one, the variation of the pinion tooth angle may be as much asfifteen or twenty degrees either way from the radial relation heretoforedefined; while for ratios of two to one, or less,l the limits ofvariation are much narrower. Such pinion may be generated and cut byknown methods, for

insta-nce in the manner and by means subi stantially as disclosed forcuttin helical gears in the patent of Edwin R. Fe ows No. 676,227, datedJune 11, 1901.

The preferred mode of forming correct tooth curves in the gear to meshwith the pinion so defined, is to generate such curves according to therinciples disclosed in the beforementioned atent No. 676,227, and in thelater patent to Fellows No. 982,551 dated January 24, 1911. In applyingthese principles we preferably use a helical cutter such as shown insaid Patent No. 676,227, having the same diameter and the same number ofteeth, with the same pitch and helix angle, as the pinion; and wepreferably mount the cutter for operation on a gear blank in a machinewhich is novel in this respect, that the axes of the spindles whereonthe cutter and gear blank are mounted have the same relation to eachother as the axes on which 'the pinion and crown gear are to bearranged, and in other respects is substantially4 like the geargenerating machine disclosed in the aforesaid Fellows Patent No.982,551. n then operating 'the machine so equipped, as explained in saidpatents, to cut teeth in a gear blank, the teeth a' of the gear aregenerated with face curves which, in all planes of section transverse tothe length of these teeth and outside of the line g, are conjugate withsubstantially mathematical accuracy to, and adapted to make correctrolling contact with, the parts of the pinion teeth which engage thegear teeth in the same planes of section.

While specific variations will be found between gears produced accordingto this invention to mesh with pinions of dierent amounts of offset,different helix an les, and (or) different ratios, certain supertigcialcharacteristics common to all species may be noted. Thus, although theteeth are more or less nearly radial to the gear, they arenot exactl so,but are curved, as 1nd1 cated by the llnes kph and ltr-lc, wluchcoincide with the bottom elements of opposite sides of the same tooth.They are, also, unsymmetrical on opposite sides, the face a3., which isturned toward the pinion when at the side of the radius c--d away fromthe axis Z22-b2, being flatter in curvature (as to its elements lying inplanes perpendicular to the axis a2) than the opposite face a4.

The teeth of the gear so characterized are long enough to have amplestrength and thelr face curves have the forms necessary for correctrolling action with, and uniform bearing on, the pinion teeth. Theiraccuracy of form andspacing enables the couple to turn at high speedWithoutv4 objectionable noise or vibration. The offset between the axesof the pinion and gear enables the couple to be used where gears whichmust turn about intersecting axes cannot be used, but as the amountofofset is less than the radius of the large gear, the invention permitsof a high gear ratio being applied in a compact arrangement where thedriving and driven shafts are relatively close together; and the factthat both sides of .the teeth may be generated in one operation makesthe cost of manufacture lower than that of gears of which the teeth mustfirst all be cut on one side and then all cut on the opposite side.

In addition to all the foregoing, the couple has the further advantagethat the pinion may be adjusted axially in either direction within widelimits, without affecting the character of mesh between the conjugateteeth. Apart from structural limitations of space imposed bycircumstances having nothing to do withthis invention, the only limitsto such adjustments are those fixed by the width of face of the pinion.

What we claim and desire to secure by Letters Patent is:

1. A gear couple consisting of a crown gear and a helical spur pinion,the axis of the pinion being transverse to the axis of the gear andbetween the latter axis and .f the tooth-bearing zone of the gear, andthe helix angle of the pinion teeth being such that the active face ofeach tooth becomes approximatel radial to the gear when such face passesthrough the middle of its arc action.

2. A skew helical crown gear having teeth formed throughout the greaterpart of their extent with mathematically correct face curves conjugateto the teeth of a helical spur pinion, of which the axis lies betweenthe center and the circumference of the gear, and the teeth when in themiddle of their arc of action are approximately radial to the gear.

3. A gear couple consisting of a helical spur pinion and a crown geararranged with non-intersecting axes, but the axis of the pinion beingwithin the circumference of the gear, the teeth of such gear beingconjugate to those of the pinion.

4. AA skew helical crown gear having teeth which are of relativelydifferent contour on opposite faces and are conjugate to the teeth of ahelical pinion whose axis is parallel to a line intersecting the axis ofthe gear and is within the circumference of the gear.

5. A skew helical crown erated teeth, the face curves of which aremathematically conjugate to the teeth of a helical pinion, the axis ofwhich is ol'set from the axis of the gear to a distance less than thecircumference of the gear.

6. A gear couple consisting of a crown gear and a helical pinionarranged on non-parallel and non-intersecting axes, the helix angle ofthe pinion tooth being such that the active face of such tooth, when inthe middle of its arc of action, approximately coincides with the radiusof the gear through the common pitch point of the couple and the teethof thv gear being conjugate to the pinion tooth so characterized.

7. A skew helical crown gear having teeth which are substantially radialand in a plane perpendicular to the axis ofthe gear, but as a whole arelongitudinally curved in such plane and are unsymmetrical on oppositelsides. v

8. A skew helical crown gear having teeth which are substantially radialand in a plane perpendicular to the axis of the gear, but as a whole arelongitudinally curved in such plane and are unsymmetrical on oppositesides, one side havin a iiatter longitudinal curvature than the ot er.

9. A gear couple, consisting of a pinion and a crown gear arrangedonnon-parallel axes offset from one another b la distance lessthanthc'pitch radius of t e gear; the pinion having spur helical teethof which the helix angle is such that the faces of said teeth becomeapproximately tangent at the common pitch point of the couple to gearhaving gen` vao the radius of the gear which p asses through this point,and the gear havmg non-symmetrical teeth of which the face toward thepinion, when at the side of said radius away from the axis of thepinion, is of flatter longitudinal curvature than the opposite face.

10. A gear couple, consisting of a pinion and a crown gear arranged onnon-parallel axes offset from one another by a distancev less than thepitch radius of the gear; the

pinion having spur helical teeth of which the helix angle is such thatthe faces of said teeth become approximately tangent at lso the commonpitch point of the couple to the tooth faces lwhich engage the gearteeth in radius of the gear Which'passes through the same planes lofSection.

this point, and the gear having teeth of 1n testimony whereof we haveaffixed our 10 which the transverse sections, in planes outsignatures.

side of a line concentric with the gear and passing through said commonpitch point7 EVERARD STUBBS.

are conjugate to .thoseparts of the pinion E. R. FELLOWS.

